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Chimps, bonobos and orangutans grasp how others view the world

You tell me what I’m thinking

Fiona Rogers/Corbis/Gett

By Emily Benson

APES may be even more like us than we thought. They appear to anticipate that a person’s actions will follow his or her beliefs, even when they know the beliefs are wrong – an ability never before demonstrated in non-human primates.

The capacity to infer what others might be thinking, known as theory of mind, is central to what makes us human, and is reflected in the ways we cooperate and communicate, says Christopher Krupenye at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

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To see whether apes have this same type of awareness, Krupenye, Fumihiro Kano at Kyoto University in Japan, and their colleagues filmed scenarios designed to stimulate apes when played to them. The videos involve conflict between pairs of human actors, one of whom is dressed in a King Kong costume.

“This most sophisticated and significant of human skills may not be unique to us“

In one video, the fake ape hits a person, and then hides in one of two haystacks while the person watches. After the human leaves the scene, “King Kong” exits the haystack and runs off-screen. The person then reappears, apparently looking for the attacker.

Because humans and other animals will look at a location where they anticipate action, the haystack that the apes glanced at first when they watched the video might indicate the one they expected the human to approach.

The researchers used a camera to track the eyes of 40 apes, including chimpanzees, bonobos and orangutans. Of the 30 that focused on the haystacks, two-thirds looked first at the one where the human falsely believed the character was hiding.

The scientists also tested the apes with a similar scenario, in which the King Kong character hides a stone in one of two boxes as a person watches, but then steals it when they leave.

When the person returns to look for the stone, about three-quarters of apes that paid attention to the boxes glanced first at the one that the human should open.

To test that the apes weren’t just looking at the last place where they saw an object or character, the researchers filmed different versions of the videos. In these, King Kong briefly hides in the other haystack after the person leaves before dashing away, or transfers the stone to the other box without a person watching (Science, doi.org/brmq).

“They can anticipate that an individual will search for an object where they last saw it, even though the apes know that it’s no longer there,” Krupenye says. “That is a really important human skill that has never been shown before in apes.”

This means that one of our most sophisticated and significant skills – reading the minds of others – is not unique to us, but also possessed by some of our evolutionary relatives, says Kano. Just like us, great apes have complex social lives bolstered by mutual understanding, he says.

Although the study demonstrates an exciting new method for testing apes’ understanding, it raises more questions than it answers, says Laurie Santos at Yale University.

“We don’t yet have a reason why primates fail other false-belief studies while succeeding on this,” she says.

One possibility is that earlier studies tested for conscious understanding, whereas the new one demonstrates implicit knowledge similar to the kind that human infants display, says Alia Martin at Victoria University of Wellington in New Zealand.

This article appeared in print under the headline “Apes can see things from the perspective of others”